In a voltage converter, PWM controller is used to regulate the output voltage of the voltage converter for supplying for an electronic apparatus. FIG. 1 shows a typical voltage converter 10, in which a high side switch 14 and a low side switch 18 are connected in series between a converter power Vin and ground GND, and a PWM controller chip 12 is connected to the switches 14 and 18 to switch them to produce an output current I flowing through an inductor L connected to a phase node 16 between the switches 14 and 18 to charge a capacitor C to produce an output voltage Vout. When the voltage converter 10 starts up, an enable signal Ve is provided to the PWM controller chip 12 through an enable pin EN on the PWM controller chip 12 to enable the PWM controller chip 12. In the PWM controller chip 12, a comparator 122 serves as a power sensing arrangement, and has its non-inverting input connected to a pin OCSET on the PWM controller chip 12 to connect to the converter power Vin through a sense resistor RS, and its inverting input connected with a reference Vinpor. When the voltage on the non-inverting input of the comparator 122 is equal to or higher than the reference Vinpor, it is determined that the converter power Vin is ready, and the comparator 122 produces an output PORE for the PWM controller chip 12 to generate signals Vc1 and Vc2 for two drivers 126 and 128 to switch the switches 14 and 18. To avoid the output current I to be so large to destroy the load circuit connected to the voltage converter 10, an over-current protection arrangement is included in the PWM controller chip 12, which comprises a comparator 124 having its non-inverting input connected to a pin PHASE on the PWM controller chip 12 to connect to the phase node 16, and its inverting input connected to the pin OCSET to connect to the converter power Vin through the sense resistor RS, and a current source 129 connected between the inverting input of the comparator 124 and ground. When the voltage on the pin OCSET is lower than the voltage on the pin PHASE, it is determined that the output current I is greater than a predetermined threshold, and the comparator 124 will produce an over-current signal OC for over-current protection.
However, in the voltage converter 10, three pins EN, OCSET, and PHASE are required on the PWM controller chip 12 for accomplishing the enable function, power sensing function, and over-current protection function, which limits the minimized size of the PWM controller chip 12 and costs more for the package of the PWM controller chip 12. Moreover, the pin OCSET is connected to the converter power Vin through the sense resistor RS, which requires the power sensing arrangement and over-current protection arrangement to use high voltage elements for implementing their circuits, thereby increasing the cost and complexity of the circuits.
Therefore, it is desired a low cost, simple, and reduced pin counts PWM controller chip for a voltage converter.